- Virus internalization or entry or penetration is the process during which viruses gain access to viral replication sites within uninfected cells, a multistep course of events that starts with binding to target cells.
- During virus entry, the genome of a virus particle is delivered to the replication site – (i) in the cytosol-on cytoplasmic membranes or – (ii) in the nucleus
- Since viruses are simple in structure/composition and lack any locomotive capacity, viruses depend on cellular trafficking mechanisms during entry, which most often involves endocytosis
- Virus entry is highly dynamic due to the following two main reasons
- The subsequent interactions of the virus with cellular structures during the various entry steps (binding, plasma membrane dynamics, internalization/endocytosis, intracellular trafficking, penetration/membrane fusion) are transient, and they require motion of the virion.
- The virus interacts with cellular structures that are dynamic themselves.
- After binding to cell-surface receptors, viruses are internalized through several mechanisms;
- Translocation of the entire virus particle across the cell membrane —–this process is relatively rare among viruses and is poorly understood
- Phagocytosis (cell eating)- occurs in specialized mammalian cells (so-called professional phagocytes, e.g., dendritic cells and macrophages) that engulf large and essential virus particles
- Viral membrane fusion – It involves the merging (fusion) of the virus membrane with the host cell membrane or at an intracellular location following virus uptake by endocytosis.
- Receptor-mediated endocytosis (viropexis): endocytic internalization mechanisms include macropinocytosis (cell drinking), clathrin-mediated endocytosis, caveolae, and clathrin- and caveolin-independent.
Further Reading